My view on this is that PD is more of a functional distinction--and perhaps that is narrowly shaped by my exposure to State--and that paradiplomacy (the awkward scholarly blanket term for this multilevel engagement) is a structural distinction. In other words, one might imagine PD conducted by a subnational unit toward another country, or another country conducting PD toward another country's subnational unit, but that would not encompass, say, trade and investment decisions carried out by subnational units.

To put it another way, I don't think that overlap here is conceptually fatal--what strikes me is the degree to which almost every activity you've just mentioned is read out of scholarly foreign policy anlaysis of the USA (to say nothing of US political scientists' analysis of the USA), whether it's classified as PD or not simply because the assumption that foreign policy (as activity and target) "belongs" to the federal government is very strongly situated. But that's not, really, how the world works--witness, for example, boycotts of private corporations in the Arab world at the moment! Rather a lot of "international" activity doesn't directly involve states and may involve actions that take place entirely within one country.

I do think that going too far from the *public* part of public diplomacy does risk stretching something, though. A diplomat talking to a church group (say) or a university audience about foreign policy does seem to me to be fundamentally different to insisting on explicit quid pro quos in the context of bargaining interactions over (say) hosting the Olympics. Or, to put it another way, speeches by the IOC committee's members urging the USA to do X or Y as Canada did would be much more readily classifiable as public diplomacy.